The present invention relates to a hydrogen generating, apparatus which uses a fuel hydrocarbon or the like and water as raw materials and gives a hydrogen gas by steam reforming of the fuel.
For producing hydrogen, there are methods of steam reforming of fuels. In these methods, fuels such as natural gas, hydrocarbons like LPG, alcohols like methanol, naphtha and the like and water are used as raw materials and the fuels are subjected to a steam reforming reaction in a reforming part or reactor equipped with a reforming catalyst to generate hydrogen. There is also provided a shifting part conventionally for shifting water and carbon monoxide since carbon monoxide is produced as a by-product in the above-described steam reforming reaction.
Further, when a steam reforming method is used for supplying hydrogen to fuel cells, particularly to a solid polymer fuel cell, a purification part utilizing a carbon monoxide oxidizing method, methanization method or the like is provided for further removal of carbon monoxide in a shifted gas passed through a shifting part. The above-described reforming part, shifting part and purification part are equipped with catalysts corresponding to respective reactions and the reaction temperatures differ depending on the catalysts, therefore, there is a need to heat respective catalysts to respective reaction temperatures for stable generation of hydrogen.
In such hydrogen generating apparatuses, the temperature in the reforming part is most high and the temperature lowers gradually in the order of the reforming part, the shifting part into which a reformed gas flows in and the purification part into which a shifted gas flow in since a heating part is provided only in the reforming part situated at the upstream side. Therefore, there has been adopted a constitution in which the shifting part and the purification part are heated sequentially with heat from the reforming part, for example, heat kept in reformed gas or surplus heat in the heating part.
In such constitution, however, a long time is required before the catalyst temperatures of respective reaction parts (reforming part, shifting part and purification part) are stabilized. Surely, there is no specific problem in a hydrogen generating apparatus which is usually operated in continuous mode used in a plant and the like since the operation can be effected while estimating the starting-up time. However, such constitution is not preferable in a hydrogen generating apparatus which effects frequent starting up and stopping and needs stable generation of hydrogen in a short period of time.
On the other hand, there is also used a method in which special heating parts are provided to respective reforming part and purification part and the starting-up time is shortened by allowing the heating parts to actuate when catalysts are heated in starting up the apparatus. This method, however, has a problem that constitution becomes complicated or the cost of the apparatus increases due to integration of the heating parts into the apparatus.
The first object of the present invention is to provide a hydrogen generating apparatus assuming daily starting-up and stopping in which the temperatures of catalysts in respective reaction parts can be stabilized in a short period of time by a simple constitution, in view of the above-described facts.
In the above-described steam reforming, hydrocarbon-based fuels such as methane, propane, gasoline, kerosene and the like are reformed at temperatures from about 500 to 800xc2x0 C., and alcohol and ether-based fuels are reformed at temperatures from about 200 to 400xc2x0 C.
In this reforming, higher the reaction temperature, higher the concentration of carbon monoxide (CO) generated, therefore, particularly when hydrocarbon-based fuel is used, a CO shifting catalyst is used and CO and steam are reacted to reduce the CO concentration down to 0.1 to 1% for example.
Particularly in the case of a fuel cell which works at a lower temperature of about 100xc2x0 C. like a solid polymer fuel cell, there is required decrease in the CO concentration down to several ppm level, hence causing use of a CO purification catalyst which selectively oxidizes CO by addition of a trace amount of air. This catalyst has been used as a catalyst body having a form of pellet such as cylindrical, spherical and the like.
However, when a catalyst body in the form of a pellet is used, there has been a problem that since the catalyst body collapses due to heat impact in each starting Lip of a fuel cell and vibration in being mounted on vehicles and the like, the catalyst can not be used until the life inherent to the catalyst component due to generated need of exchange with a novel catalyst body. There has been also a possibility that a catalyst powder produced by collapsing of the catalyst body obstructs the fuel flow route of a fuel cell.
Namely, conventional hydrogen generating apparatuses have no large problem in uses wherein only stationary operation is conducted in chemical plants and the like and frequent starting up operation is not required, however have problems in uses wherein stopping of operation and starting up are repeated and vigorous vibration occurs such as in fuel cells for domestic use or for vehicle use.
The second object of the present invention is to provide a hydrogen generating apparatus which can allow the ability of a catalyst body to be fully manifested and can provide utilization of the full life of the catalyst body, causing stable operation for a long period of time, even in uses wherein stopping of operation and starting up are repeated and vigorous vibration occurs, in view of the above-described facts.
Further, conventional hydrogen generating apparatuses which provide generation of hydrogen by the above-described steam reforming have no means provided between these reforming catalyst body, CO shifting catalyst body and CO purification catalyst body to prevent catalyst components from scattering.
When means to prevent scatter of a catalyst are not provided, there is a possibility that heat impact is applied to a catalyst body in starting up the hydrogen generating apparatus, a catalyst body collapses due to vibration when placed on vehicles, and when used for a long period of time, fallen catalyst components fly to the downstream side of a catalyst body.
In this case, the scattered reforming catalyst methanizes a reformed gas, the scattered CO shifting catalyst prevents selective oxidation of CO and increases the CO concentration by a reverse shift reaction, providing a factor causing reduction in efficiency of the whole apparatus.
Thus, conventional methods have no large problem in uses wherein only stationary operation is conducted in chemical plants and the like and frequent starting up operation is not required, however have a lot of problems in uses wherein stopping of operation and starting up are repeated and vigorous vibration occurs such as in fuel cells for domestic use or for vehicle use.
The third object of the present invention is to provide a hydrogen generating apparatus which eliminates influence by scatter of a catalyst body and operates in a stable manner for a long period of time, for solving the above-described problems of hydrogen generating apparatuses, in view of the above-described facts.
The present invention provides, for first attaining the above-described first object, a hydrogen generating apparatus comprising a fuel feeding part, a water feeding part for fuel reforming, an oxidant gas feeding part, a reforming catalyst body, a heating part for the above-described reforming catalyst, a CO shifting catalyst body and a CO purification catalyst body and in which the reforming catalyst body, the CO shifting catalyst body, the CO purification catalyst body being placed sequentially in this order form the above-described fuel feeding part toward the downstream side, wherein a fuel and water are fed to the above-described reforming part which has been heated, an oxidant gas from the above-described oxidant gas feeding part is mixed with each of the above-described reformed gas introduced into the above-described shifting part and a shifted gas obtained in the above-described shifting part and introduced into the above-described purification part, and at least a part of the above-described reformed gas and at least a part of the above-described shifted gas are oxidized respectively in the above-described shifting part and the above-described purification part.
The above-described fuel feeding part and the water feeding part may be integrated, and the CO shifting catalyst is a catalyst which allows shift reaction of water and carbon monoxide.
In this case, it is preferable that a shifting catalyst of the above-described shifting catalyst body contains as one component at least a platinum group-type catalyst.
Further, it is preferable that a hydrogen generating apparatus has a shifting catalyst temperature measuring part which measures the temperature of the above-described shifting catalyst body and the temperature of the shifting catalyst is controlled by controlling the amount of an oxidant gas to be mixed with the above-described reformed gas.
Furthermore, it is preferable that a hydrogen generating apparatus has a purification catalyst temperature measuring part which measures the temperature of the above-described purification catalyst body and the temperature of the purification catalyst is controlled by controlling the amount of an oxidant gas to be mixed with the above-described shifted gas.
Still further, it is preferable that an oxidant gas from the above-described oxidant gas feeding part is mixed with a fuel and water from the above-described fuel feeding part and the water feeding part.
Moreover, it is preferable that a hydrogen generating apparatus has a reforming catalyst temperature measuring part which measures the temperature of the above-described reforming catalyst body and the temperature of the reforming catalyst is controlled by controlling the amount of an oxidant gas to be mixed with the above-described fuel and water.
In the hydrogen generating apparatus of the present invention, it is preferable, for attaining the above-described second object, that the reforming catalyst body, CO shifting catalyst body and CO purification catalyst body comprise a carrier or support having a honeycomb structure, foamed body structure or corrugated structure which carries a catalyst component.
It may be advantageous that a hydrocarbon fuel, alcohol fuel or ether fuel is fed from the above-described fuel feeding part.
Further, it is preferable that the above-described water feeding part for fuel reforming feeds also air together with steam.
Also, it is preferable that the above-described water feeding part for fuel reforming feeds only air.
As materials constituting the above-described carrier, heat-resistant inorganic materials, metals and heat-conductive inorganic materials are exemplified. Further, the above-described carrier may be constituted of a complex material composed of heat-resistant inorganic materials and metals or heat-conductive inorganic materials.
Furthermore, the hydrogen generating apparatus of the present invention has, for attaining the above-described third object, the above-described scatter preventing means provided at least between the above-described reforming catalyst body and the above-described CO shifting catalyst body or between the above-described CO shifting catalyst body and the above-described CO purification catalyst body.
It is preferable that the above-described scatter preventing means is a filter and a pressure detecting apparatus which detects pressure loss caused the above-described filter is placed at the upstream side and at the downstream side of the above-described filter.
As the above-described filter, filters are exemplified constituted of fiber composed of a metal, ceramics or complex thereof. There can also be used filters composed of a metal, ceramics or complex thereof in the form of mesh, honeycomb or foam.
In the hydrogen generating apparatus of the present invention, it is preferable that the temperature of the above-described filter is higher than the temperature at which a reformed gas is methanized.
Further, it is preferable that a temperature detecting apparatus is provided at a position near the above-described filter.